1. Field of the Invention
The invention relates to a surgical instrument, to a method for measuring the local mechanical resistance of a porous body and to the use of the surgical instrument for estimating the quality of cancellous bone.
Known probes for measuring the mechanical resistance of porous bone commonly comprise a cannulated probe that is slid on a K-wire previously inserted in the bone. However, during insertion the K-wire is mostly slightly deformed resulting in a variable contact area between the K-wire and the inner surface of the cannulation of the probe. The larger being the contact area between the K-wire and the probe the more being the K-wire deformed (resulting in a force component normal to the inner probe surface) the higher is the friction between the K-wire and the probe. The higher the friction between probe and the K-wire is the higher will be (artificially) the recorded torque. The lower the bone mineral density is the higher is the weight of this bias. Disregarding this varying frictional torque can lead the surgeon to take a wrong decision.
2. Description of the Related Art
From WO 2008/052367 a device for determining the local mechanical resistance inside of a porous body having a variable density and/or porosity is known. This known device comprises a tool with a shank having a tip with blades that allow to measure the local mechanical resistance of the porous body after pushing the tip into a porous structure at the bottom of a predrilled hole and rotating the tool about its longitudinal axis. Particularly, when measuring the local mechanical resistance of porous bone in the cancellous bone tissue a bore hole has to be predrilled through the harder cortical bone tissue surrounding the cancellous bone tissue. Therefore, this known device shows the disadvantage that a hole has to be previously drilled into the bone by using a separate tool.